The Big Picture: Variation in animal reproduction exists


  • Mating between single male and female is boring
    • species can reproduce without fertilization
    • individual of species can change sex
    • species can have both male and female sex organs
    • some populations have only a few that mate


  • Two modes of reproduction in animal kingdom
    1. Sexual:
    2. Asexual:


  • Animals exhibit cycles of reproductive activity


  • Mammalian reproduction is governed by hormones

Asexual reproduction in the animal kingdom


  • Budding:
    • found among invertebrates


  • Fission:
    • about the same size
    • found among invertebrates


  • Fragmentation:
    • accompanied by regeneration of lost body parts
    • sponges, worms, starfish


  • Parthenogenesis:
    • found among invertebrates and vertebrates

Parthenogenesis: Male drone bees are fertile and haploid!


Parthenogenesis in Charlotte the stingray?!?!?!?!?!


Animal reproduction blurs the lines of male and female



  • Sexual reproduction commonly between male and female
    • but finding a partner may be difficult


  • Stationary/slow animals can be hermaphroditic
    • individual have male and female reproductive bits
    • Any 2 individuals can mate


  • Sex reversal occurs in different animal phyla
    • oysters are males first, then turn to female when larger
    • the largest female in some coral fish turn to male

Reproductive cycles are common in the animal kingdom



  • Cycles controlled by hormones and environmental cues
    • occur with asexual or sexual modes
    • often related to seasons


  • Ovulation: release of eggs at midpoint of female cycle
    • cycles are variable in length
    • sheep: cycle + pregnancy = birth in spring


  • Daphnia: cycles between asexual and sexual
    • seasonally related to environment
    • asexual when environments are stable….

The “Handicap” of sexual reproduction


How sperm and egg come together…





  • Fertilization = Fusion of haploid gametes
    • external:
    • internal:



  • Moist habitat always required for external fertilization
    • spawning: when many individuals release gametes at the same time and place

How sperm and egg come together…





  • Fertilization = Fusion of haploid gametes
    • external:
    • internal:



  • Pheromones: chemicals used to influence physiology and behavior
    • function as mate attractants
    • volatiles can be detected over long distances
    • pheromone production in humans is controversial

Pheromones in humans?


Internal vs External: Offspring survival




  • Internal fertilization produces fewer gametes
    • survival of embryos higher


  • Internal associated with protection mechanisms
    • parental care of young
    • shells, amniotic eggs, marsupials


  • Parental care not just in vertebrates..


  • External fertilization produces more offspring with lower survival rates

Making and delivering gametes




  • Animals usually have gonads that produce gametes
    • testes in males, ovary in females
    • often established early in embryo development


  • Many animals also have accessory organs
    • structures to carry, store, protect and nourish gametes
    • e.g. fruit fly (spermathecae stores sperm in female)


  • Mating may occur with more than 1 male
    • males have mechanisms to prevent other male success

Mammalian reproduction reproduction governed by hormones




  • Hormones coordinated across many glands/organs
    • hypothalamus, pituitary and gonads
    • endocrine system chemical messaging


  • Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus (a region of the brain)
    • directs release of FSH (follicle-stimulating hormone)
    • directs release of LH (luteinizing hormone)
    • both from pituitary gland


  • FSH and LH act on male and female gonads
    • stimulate reproductive hormone production

Mammalian reproduction system governed by hormones



  • Gonads then produce and secrete 3 hormones
    • testosterone, estrogen and progesterone
    • found in male/females in different amounts


  • Embryos: develop reproductive structures


  • Maturing mammals: induce sex characteristics
    • physical/behavior differences (male/female)
    • ‘Puberty’


  • Mature mammals: play role in gamete formation and reproductive cycles

Hormonal control of male system (negative feedbacks)


Most female mammals have an ovarian cycle



  • Some females have linked menstrual cycle
    • 10 primates, elephant shrew, some bats, spiny mouse


  • Ovarian cycle: series of changes in ovaries for maturation and release of eggs


  • Menstrual cycle: prepares uterus for pregnancy
    • endometrium thickens with blood vessels
    • preparation for embryo implantation
    • if embryo does not implant, endometrium is shed


  • Both cycles occur concurrently using same series of hormones